The field of the invention is synthetic resins from polyhydric alcohol-polycarboxylic acid reaction products. The invention is particularly related to a method of preparing pilling-resistant fiber products from polyesters containing 0.05 - 5.0 molar percent, based on the acid component, of dicarboxylic acid groups which contain acetal groups and/or of a diol which contains acetal groups.
The state of the art of the present invention may be ascertained by reference to the Kirk-Othmer "Encyclopedia of Chemical Technology", Vol. 16 (1968), pages 143-159, under the section entitled "Polyester Fibers"; U.S. Pat. Nos. 3,335,211 and 3,391,123 which show the state of the art of improving the pilling effect of polyester fibers; and U.S. Pat. No. 2,945,008 which shows the preparation of the polyesters used in the present invention.
U.S. Pat. No. 2,945,008 discloses the preparation of a high melting linear highly polymeric condensation polymer of (A) at least one bifunctional compound selected from the group consisting of carbonic acid, a dicarboxylic acid containing from 2 to 20 carbon atoms and an organic diisocyanate containing from 6 to 23 carbon atoms, and (B) at least one bifunctional glycol composed of from 50 to 100 mole percent of a spiro glycol having the following formula: ##STR1## and from 0 to 50 mole percent of an aliphatic glycol having from 2 to 12 carbon atoms, the relative proportions of (A) and (B) constituents being such as to constitute a polymer selected from the group consisting of polyesters and polyurethanes, which polymer melts at between about 150.degree. C and about 270.degree. C.
Threads and fibers of polyethylene terephthalate have gained great importance in the clothing industry due to the large number of excellent properties, such as a high melting point, resistance to chemicals, heat, hot water, and light, as well as their mechanical properties.
However, besides the numerous advantages, polyester fibers also exhibit disadvantages. One of these is the so-called pilling effect. The latter originates from the fact that during the wearing of such fabrics, threads are pulled out of the fabric structure and are twisted into little balls fixedly anchored in the fabric. These pills impart an unattractive appearance to the fabric surface and thereby impair the quality of the respective garment.
A great number of attempts have been made in the past to overcome this disadvantage inherent in the polyester by means of various measures.
The prior art process most frequently employed resides in reducing the molecular weight of the polyester, with correspondingly reduced specific viscosities (abbreviated hereinbelow as RSV) of about 0.35 - 0.45 dl./g. (measured in phenol/tetrachloroethane 60/40 at 25.degree. C) and a concomitant decrease in the tensile strength of the thread as disclosed in Japanese Patent Application 24 932/65. However, the melt spinning of such a material causes considerable difficulties, since the melt is of a very thinly fluid consistency.
Another possibility resides in producing polyesters containing monomeric compounds, such as alcohols or carboxylic acids with three or more functional groups, e.g., glycerin, pentaerythritol, or trimesic acid, as disclosed in German Published Application 1,928,436. In this method, partially branched polyesters are obtained which, as compared with their molecular weight, have a higher melt viscosity than is the case in strictly linear products.
Also, several attempts have been made to chemically weaken polyester fibers as well as fabrics manufactured therefrom subsequently, by treating the same with water, soda, ammonia, hydrazine, amines, carboxylic acids, or alcohols at elevated temperatures, as disclosed in Czechoslovakian Pat. 108,689; Dutch Pat. No. 91,330; French Patent 1,551,050; Japanese Pat. No. 7,122,174; and German Published Application 1,024,482. However, it was found that such a degradation can be controlled and/or made reproducible only with difficulty. In many prior art cases, attempts have been made to generate weakened sites in the molecule where subsequently a hydrolytic cleavage is effected by the incorporation of chain members with hetero atoms, especially silicon, as disclosed in U.S. Pat. No. 3,335,211 and German Published Application 1,273,123; boron, as disclosed in U.S. Pat. No. 3,391,123 and German Published Application 1,469,127, or aluminum as disclosed in German Published Application 1,545,039, which also leads to branching of the chain. Even in this hydrolytic cleavage process, the reproducibility of the results meets with difficulty. Besides, it is necessary to operate under absolutely anhydrous conditions until the point of time where the desired hydrolytic degradation takes place. It is generally known that this aspect causes particular difficulty. The conventional prior art processes thus are not as yet satisfactory in all respects.